1. Field of the Invention
This invention relates to an ethylene resin composition comprising an ethylene polymer, or a copolymer of ethylene and a component(s) copolymerizable with ethylene, and alumina trihydrate having a gibbsite crystal structure.
2. Description of the Prior Art
Resin compositions comprising more than 100 parts by weight of various reinforcing inorganic fillers per 100 parts by weight of olefinic polymers, such as ethylene polymers or propylene polymers, are well known in the art as disclosed in, for example, Japanese Pat. Publication No. 29377/71 and British Pat. No. 93,6057.
Although these resin compositions can be obtained at low cost and more improved in certain physical properties, these resin compositions have disadvantages in that the fillers lower the inherent physical properties of moldings produced from such resin compositions and it is very difficult to incorporate a large amount of inorganic fillers, e.g., more than 70% by weight based on the weight of the olefinic polymers. Further, it is difficult to obtain moldings having a uniform composition from a mixture of olefinic polymers and inorganic fillers even if a large amount of fillers could be incorporated into the olefinic polymers. In thermoplastic resins generally used, it is also necessary to use fillers having low cost in order to avoid economical problems.
Compositions comprising olefinic polymers and above reinforcing inorganic fillers, for example, .beta.-type alumina hydrate as disclosed in Japanese Patent Publication No. 8037/65, show high modulus, tensile strength and hardness, but they also exhibit low flexibility, tear strength and toughness. When smaller proportions of inorganic fillers are used in these compositions to eliminate the above disadvantages, the flexibility and tear strength are improved to a certain degree but mixing costs increase, and economically advantageous products cannot be obtained. Further, when proportions of inorganic fillers are decreased, i.e., the olefinic polymers are used in a large proportion, the products obtained from such resin compositions evolve considerable heat when they are subjected to combustion, e.g., when burned as a rubbish after use, and such products give forth large volumes of black smoke or soot during combustion. In addition, these products are readily flammable and are not suitable for use as structural materials.
Resin compositions comprising a large proportion of alumina trihydrate having a gibbsite crystalline structure are excellent in flexibility, and sheets or films produced from such compositions generally retain a waxy feeling on their surfaces but are not said to be excellent in marking and printing properties. This is due to the fact that the surfaces of the sheets or films lack roughness and/or a hydrophilic property in view of the nature of lipophilic thermoplastic resins. Further, a composition comprising a thermoplastic resin and aluminum hydroxide, which has been subjected to removal of free water and subsequently dried (obtainable from sodium aluminate in the production of alumina hydrate (aluminum hydroxide)) generally exhibits poor dispersibility because of partial aggregation of the particles, and moldings produced from such a composition sometimes have undesirable spots on the surfaces of the moldings and lack a uniform hydrophilic property.
In order to improve the hydrophilic property, a method comprising immersing the moldings in an aqueous solution of sodium hydroxide having a high concentration or in concentrated sulfuric acid at high temperature and for a long period of time to elute the aluminum hydroxide contained in the moldings has been proposed. Though this method improves the printing and marking properties of the moldings to a certain extent, it also deteriorates or deforms the moldings and adversely affects the mechanical properties of the moldings since the moldings are subjected to severe conditions.
The present invention also contemplates a bonded laminate comprising moldings of the resin composition of the present invention and articles of metals. Bonded laminates of this type are now widely used in transportation facilities such as vehicles, ships and the like and in structural materials. These bonded laminates have various advantages such as lightness, good corrosion resistance, and good, heat insulation capability, as well as being inexpensive, all of which are characteristic features inherent in thermoplastic resins. The bonded laminates also have excellent mechanical properties such as impact strength and toughness which are characteristic features inherent in metals.
More recently, the demand for bonded laminates having excellent heat-resistance and non-flammability in addition to the above advantages has steadily increased in the architectural field. However, it was well known that thermoplastic resins such as polyolefin resins, e.g., polyethylene resin, polypropylene resin, etc., cannot be effectively bonded to metals. Various processes have heretofore been proposed for bonding thermoplastic resins to metals, for example, a process for activating the surface of the thermoplastic resins by ionization with .gamma.-rays, ozone oxidation or high temperature treatment (for example, see Japanese Pat. Application Publication No. 11836/63), a process comprising subjecting polyethylene to thermal degradation and subsequently modifying it with maleic anhydride (for example, see Japanese Pat. Application Publication No. 8728/69), a process comprising modifying polypropylene with maleic anhydride (for example, see Japanese Pat. Application Publication No. 10757/1967) and a process comprising using a graft copolymer (for example, see Japanese Pat. Application Publication No. 27235/1970).
These prior art processes do, in fact, improve the adhesiveness of thermoplastic resin moldings to other articles to a certain extent, but they are accompanied with some disadvantages in that adhesiveness is still insufficient, complicated operations are required for adhesion, and the adhesion requires a long period of time.
Generally speaking, the adhesiveness of olefin resin compositions to other materials is not satisfactory and, in adhering moldings of an olefin resin composition to articles of other materials, for example, metals, it is necessary to use an adhesive between the articles to be bonded and to apply pressure to bond.
It was also well known that prior art resin compositions as disclosed in, for example, Japanese Pat. Application Publication Nos. 8037/1965 and 28199/71 are useful as materials for electric parts, industrial parts, miscellaneous goods and architectural structures, but they are not satisfactory from the viewpoint of heat accumulation and heat insulation.
As a result of research to develop ethylene resin compositions containing a large amount of inorganic filler, it was found that an ethylene resin composition comprising as main components an ethylene polymer and alumina trihydrate is excellent for a wide variety of applications.
As a result of further investigations on the above ethylene resin composition, it was found that a resin composition which is suitable for use in a wide number of fields could be obtained by varying the proportion of ethylene polymer and alumina trihydrate, incorporating other materials into the resin composition according to the end use need and/or subjecting the resin composition to surface treatments, and that an excellent laminate can be obtained by heat pressing moldings of the above resin composition and articles of metal, e.g., aluminum.